In order to establish earthquake-proof performance of conventional reinforced concrete columns, research works in relation to methods for retrofitting the concrete columns has been advanced for quite a long time, and accordingly, the various results of the research works is published.
As representative seismic retrofitting methods, there are a retrofitting method using a steel plate, and a retrofitting method using a strip band of composite materials such as GFRP (Glass Fiber Reinforced Plastic), CFRP (Carbon Fiber Reinforced Plastic) or the like.
For the retrofit using the steel plate, a grouting process is substantially performed between surfaces of the steel plate and the concrete, and accordingly, there is a problem that a shape of an external and a shape of reinforced concrete column may be changed.
Also, the retrofitting method using the composite materials such as GFRP or CFRP uses adhesives such as an epoxy or the like in order to bond the composite materials. In this case, there is a problem that the retrofitting effect may be decreased because Young's modulus of the adhesives is very small.
In order to overcome the drawbacks, “a retrofitting method for compressing a steel plate using an external pressure” is recently developed. The method may be performed without a grouting process, and the method have the high effect of reinforcing due to not having soft materials such as the epoxy on surfaces of the reinforcing plate and the concrete. In addition, the method has the advantage that a lateral pressure applied from an external may increase an entire resisting force of the reinforced concrete column by withstanding a crack and breakdown of the concrete.
FIG. 1 illustrates a retrofitting method for a reinforced concrete column according to the prior art.
Referring to FIG. 1, in the conventional retrofitting method, a steel plate 10 with a prescribed thickness is firstly manufactured to form a cylindrical shape, and, then, the steel plate 10 is installed to wrap a circumference of a reinforced concrete column 100.
After the steel plate 10 is installed to wrap a circumference of a reinforced concrete column 100, a lateral pressure is applied from the outside using a compress machine commonly available in relevant fields that may use a clamp or a band plate, and, then, the steel plate 10 is compressed on the surface of the reinforced concrete column 100 by the lateral pressure.
Then, an edge surface of the steel plates 10 opposite to each other is welded to be tightly attached using a welding process such as a Tungsten Inert Gas (TIG) welding process.
Next, a welded portion of the edge surface A is grinded to flat by a grinder, and a strip-shaped steel plate 20 is welded to reinforce at welded surface so as to prevent the breakdown of the welded portion.
In case of using the above-mentioned steel plate 10, since the process for compressing the steel plate 10 on the reinforced concrete column 100 is inevitably performed, the retrofit effect may be affected by the thickness of the steel plate 10 and the welding performance of the edge surface. If the retrofitting has the same effect, it is a matter of course that the retrofit should be excellent in constructability, workability and economical efficiency.
Although its constructability is better if the thickness of the steel plate is thin, the retrofit have little effect if a cross-sectional size of the concrete column is large. On the other side, although the retrofit have an effect if the thickness of the steel plate is thick, its constructability becomes worse since the lateral pressure for compressing must be more applied. Therefore, in the retrofitting method for compressing the steel plate 10 on the reinforced concrete column 100 using the external pressure, it is very important that the optimum thickness of the steel plate 10 is determined, but it is very difficult that the thickness of the steel plate 10 is determined in a practical manner.